Fix `clippy::empty_enum` triggering on nightly with `feature(never_type)` enabled #799

Job	Run time
compilation-benchmarks	2m 4s
runtime-benchmarks (args_3)	50s
version-sync	2s
runtime-benchmarks (args_5)	51s
runtime-benchmarks (args_10_alloc)	48s
cargo-fmt	16s
cargo-doc (ubuntu)	20s
runtime-benchmarks (args_10_structs)	54s
cargo-lock	6s
cargo-doc (windows)	1m 26s
runtime-benchmarks (args_10)	53s
cargo-doc (macos)	40s
cargo-machete	4s
runtime-benchmarks (args_20)	54s
cargo-miri	1m 43s
prettier	7s
taplo-fmt	2s
test-msrv (ubuntu)	54s
test-stable (ubuntu)	1m 22s
test-msrv (windows)	1m 30s
test-unstable (beta)	28s
test-msrv (macos)	1m 0s
typos	4s
test-unstable (nightly)	30s
test-stable (windows)	3m 25s
test-stable (macos)	1m 21s
website-build	26s
	23m 0s

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